1. Field of the Invention
This invention relates generally to wireless communication and more particularly to a method for targeting the delivery of a SMS (Short Message Service) message for a mobile station to a particular base transceiver station serving the current location of the mobile station.
2. Description of Related Art
Cellular wireless is an increasingly popular means of personal communication in the modern world. People are using cellular wireless networks for the exchange of voice and data over cellular telephones, Personal Digital Assistants (“PDAs”), cellular telephone modems, and other devices. In principle, a user can seek information over the Internet or call anyone over a Public Switched Telephone Network (“PSTN”) from any place inside the coverage area of the cellular wireless network.
In a typical cellular wireless system, an area served by the wireless provider is divided geographically into a number of cells, each defined by a radio frequency (“RF”) radiation pattern from a respective base transceiver station (“BTS”) antenna. The BTS antennae in the cells are in turn coupled to a base station controller (“BSC”), which is then coupled to a telecommunications switch or gateway, such as a mobile switching center (“MSC”) for instance. The MSC or gateway may then be coupled to a telecommunications network such as the PSTN (public switched telephone network) or the Internet.
When a mobile station (such as a cellular telephone, pager, or appropriately equipped portable computer, for instance) is positioned in a cell, the mobile station communicates via an RF air interface with the BTS antenna of the cell. Consequently, a communication path is established between the mobile station and the telecommunications network, via the air interface, the BTS, the BSC and the MSC.
With the explosive growth in demand for wireless communications, the level of call traffic in most cell sites has increased dramatically over recent years. To help manage the call traffic, each cell in a wireless network may be further divided geographically into a number of sectors (which can be visualized conceptually as pie pieces). Each cell sector is defined respectively by radiation patterns from directional antenna components of the respective BTS, or by respective BTS antennae.
In a Code Division Multiple Access (“CDMA”) wireless network, each cell employs one or more carrier frequencies, and each sector is distinguished from adjacent physical sectors by a pseudo-random number offset (“PN offset”). Further, each sector can concurrently communicate on multiple different channels, distinguished by “Walsh codes”. When a mobile station operates in a given sector, communications between the mobile station and the BTS of the sector are carried on a given frequency and are encoded by the sector's PN offset and a given Walsh code.
According to industry standard IS-2000 (published in March 2000 as TIA/ELA/IS-2000-A) and IS-95, a mobile station can communicate with a number of “active” sectors at a time. Depending on the system, the number of active sectors can be up to three or six (currently). The mobile station receives largely the same signal from each of the active sectors and, on a frame-by-frame basis, selects the best signal to use.
A mobile station maintains in its memory a list of the sectors in its “active” set. In addition, it maintains in its memory a list of “candidate” sectors (up to six), which are those sectors that are not yet in the active set but that have sufficient signal strength that the mobile station could demodulate signals from those sectors. Further, the mobile maintains a list of “neighbor” sectors, which are those sectors not in the active set or candidate set but are in close vicinity to the mobile station. All other possible sectors are members of a “remaining” set.
In the existing art, when an MSC receives a termination request seeking to connect a call to an idle mobile station that is currently being served by a particular MSC, the MSC responsively directs all of the BSCs within the MSC's serving system to broadcast a general page message to the mobile station. In other words, the general page message is broadcast on the paging channel in every one of the cell sectors within the MSC's serving area. This is an inefficient use of radio resources, since the idle mobile station is at any moment operating in only a single cell sector, not in all of the cell sectors of the MSC's serving area. Similarly, when an SMS message is to be sent to a mobile station, the SMS message is sent to all BTS that are within an MSC's serving area.
It is also known for a MSC to receive a request to connect a call to a mobile station and for the MSC to responsively check with a home location register (HLR) to determine the serving area (cell and sector) in which the mobile device is currently registered to operate, and to then page the mobile station just in the cell/sector. However, the HLR record of where a mobile device is currently registered could become outdated. For example, the HLR might receive a registration record (and therefore update its database) when the mobile station enters a new MSC's serving area, but the HLR might not then receive a registration update as the mobile station moves from cell sector to cell sector within that serving area. Consequently, with the HLR database either inaccurate or not up-to-date, it may not be possible to target a page in a given cell and sector and have the page reach the mobile station.
Blanket paging of the mobile station (and blanket broadcasting of SMS messages) across all of the BSC in the MSC's serving area is largely wasteful of RF resources, since most of the paging or SMS messages would be of no effect because the mobile station is only in one cell and sector (assuming no overlap between cells).